Method and device for determining the quality of a speech signal

• US 20040078197A1
• Filed: 11/25/2003
• Published: 04/22/2004
• Est. Priority Date: 03/13/2001
• Status: Active Grant

• Current Assignee: Koninklijke KPN NV
• Original Assignee: Koninklijke KPN NV
• Inventors: Hekstra, Andries Pieter, Beerends, John Gerard
• Granted Patent: US 7,624,008 B2
• Time in Patent Office: Days
• US Class Current: 704/225
• CPC Class Codes: G10L 25/69 for evaluating synthetic or decoded voice signals

Abstract

Objective measurement methods and devices for predicting perceptual quality of speech signals degraded in speech rocessing/transporting systems may have poor prediction results for degraded signals including extremely weak or silent portions. Improvement is achieved by applying a first scaling step in a pre-processing stage with a first scalins factor (S(Y+Δ), which is a function of the reciprocal value of the power of the output signal increased by an adjustment value (Δ), and by a second scaling step with a second scaling factor (S^α(Y+Δ); S^αi(Y+Δ_i), with i=1, 2), which is substantially equal to the first scaling factor raised to an exponent having a adjustment value (α) between zero and one. The second scaling step may be carried out on various locations in the device. The adjustment values are adjusted using test signals with well defined subjective quality scores.

Claims

1. Method for determining, according to an objective speech measurement technique, the quality of an output signal (Y(t)) of a speech signal processing system with respect to a reference signal (X(t)), which method comprises a main step of processing the output signal and the reference signal, and generating a quality signal (Q),

wherein the processing main step includes:

a first scaling step (S(Y+Δ

);

S(Y+Δ

_i), with i=1,2) for scaling a power level of at least one signal of the output and reference signals by applying a first scaling factor which is a function of a reciprocal value of a first power related parameter of the at least one signal, and

a second scaling step carried out by applying a second scaling factor (S^α

(Y+Δ

);

S<sup>α

i</sup>(Y+Δ

_i), with i=1,2;

V<sup>α

3</sup>(Y+Δ

₃, t);

V<sup>α

3</sup>(Y+Δ

₃)) which is a function of a reciprocal value of a second power related parameter of the at least one signal, using at least one adjustment parameter (α

,A;

α

_i,Δ

_i with i=1,2;

α

₃,Δ

₃).

2. Method according to claim 1, wherein the reciprocal value of the second power related parameter is raised to an exponent with a value corresponding to a first adjustment parameter (α

;

α

_i with i=1,2;

α

₃), the second power related parameter being increased with a value corresponding to a second adjustment parameter (Δ

;

Δ

_i with i=1,2;

Δ

₃).

3. Method according to claim 1 or 2, wherein the first scaling factor (S(Y+Δ

);

S(Y+Δ

_i), with i=1,2) is a function of the first power related parameter increased by a value corresponding to a third adjustment parameter (Δ

;

Δ

_i, with i=1,2).

4. Method according to any of the claims 1,-,3, wherein the second scaling step is carried out on the output and reference signals (Y_S(t), X_S(t)) as scaled in the first scaling step.

5. Method according to claim 4, wherein the first and second scaling steps are combined to a single scaling step by applying the product of the first and second scaling factors.

6. Method according to any of the claims 1,-,3, wherein the second scaling step is carried out on at least one of two signals, the two signals being a differential signal (D) as determined in a signal combining stage (50.3) of the processing main step and the quality signal (Q) as generated by the processing main step.

7. Method according to any of the claims 3,-,6, wherein the second scaling factor (S^α

(Y+Δ

);

S<sup>α

i</sup>(Y+Δ

_i), with i=1,2) is derived from the first scaling factor (S(Y+Δ

);

S(Y+Δ

_i), with i=1,2), the first and second power related parameters being the same, and the second and third adjustment parameters being the same.

8. Method according to any of the claims 3,-,7, wherein the first power related parameter includes the average power of the output signal increased by an adjustment value corresponding to the third adjustment parameter (Δ

;

Δ

_i, with i=1,2).

9. Method according to claim 8, wherein increasing by said adjustment value is achieved by adding to the output signal (Y(t)) a noise signal having an average power corresponding to the third adjustment parameter (Δ

;

Δ

_i, with i=1,2).

10. Method according to any of the claims 1,-,7, wherein the first power related parameter includes a total time duration during which the power of the output signal is above or equal to a threshold value.

11. Method according to claim 10, wherein the total time duration in said first power related parameter is increased by a value corresponding to the third adjustment parameter (Δ

;

Δ

_i with i=1,2).

12. Method according to claim 10, wherein during the main processing step the reference and output signals are processed using time frames, and the total time duration in said first power related parameter is expressed by the total number of time frames during which the power of the reference and output signals is at least equal to the threshold value.

13. Method according to claim 12, wherein said total number of time frames is increased by a value corresponding to the third adjustment parameter (Δ

;

Δ

_i with i=1,2).

14. Method according to any of the claims 2,-,13, wherein the first adjustment parameter has a value between zero and one (α

;

α

_i with i=1,2;

α

₃).

15. Method according to any of the claims 3,-,14, wherein in the first scaling step the reference signal (X(t)) is scaled by applying a third scaling factor (S(X+Δ

);

S(X+Δ

_i), with i=1,2) which is derived from the reference signal using the second adjustment parameter (Δ

;

Δ

_i, with i=1,2) in a similar way as the first scaling factor is derived.

16. Method according to any of the claims 2,-,12, wherein in the first scaling step the output signal (Y(t)) is scaled, the first scaling factor (S(Y+Δ

);

S(Y+Δ

_i), with i=1,2) being a multiplication of a fourth scaling factor and a fifth scaling factor, the fourth scaling factor being a function of the reciprocal value of the average power of the output signal increased by a first adjustment value corresponding to the second adjustment parameter (Δ

;

Δ

_i), and the fifth scaling factor being a function of the reciprocal value of the total time duration during which the power of the output signal is above or equal to the threshold value increased by a second adjustment value corresponding to the second adjustment parameter (Δ

;

Δ

_i).

17. Method according to claim 6, wherein the second power related parameter of the second scaling factor (V^α

3(Y+Δ

₃,t);

V<sup>α

3</sup>(Y+Δ

₃)) includes an instantaneous value of the power of the output signal increased by an adjustment value corresponding to the second adjustment parameter (Δ

₃).

18. Method according to claim 17, wherein a local version (V^α

3(Y+Δ

₃,t)) of the second scaling factor is applied to the differential signal (D).

19. Method according to claim 17, wherein a global version (V^α

3(Y+Δ

₃)) of the second scaling factor is applied to the at least one of two signals (D;

Q).

20. Method according to any of the claims 17-19, wherein the second scaling step is combined with a third scaling step by applying a third scaling factor (S^α

(Y+Δ

);

S<sup>α

i</sup>(Y+Δ

_i) , with i=1,2) derived from the first scaling factor (S(Y+Δ

);

S(Y+Δ

_i), with i=1,2).

21. Device for determining, according to an objective speech measurement technique, the quality of an output signal (Y(t)) of a speech signal processing system (10) with respect to a reference signal (X(t)), which device comprises:

pre-processing means (12) for pre-processing the output and reference signals,

processing means (13, 14) for processing signals pre-processed by the pre-processing means and generating representation signals (R(Y), R(X)) representing the output and reference signals according to a perception model, and

signal combining means (15, 16) for combining the representation signals and generating a quality signal (Q),

the pre-processing means including first scaling means (21;

31, 32;

41, 42) for scaling a power level of at least one signal of the output and reference signals (Y(t), X(t)) by applying a first scaling factor (S(X,Y);

(S(P_f,Y);

S(Y+Δ

)), which is a function of a reciprocal value of a first power related parameter of the at least one signal,

wherein the device further comprises second scaling means (43, 44;

51;

52;

61;

62) for a scaling operation carried out by applying a second scaling factor (S^α

(Y+Δ

);

S<sup>α

i</sup>(Y+Δ

_i), with i=1,2;

V<sup>α

3</sup>(Y+Δ

₃,t);

V<sup>α

3</sup>(Y+Δ

₃)), the second scaling factor being a function of a reciprocal value of a second power related parameter of the at least one signal, using at least one adjustment parameter (α

,Δ

;

α

_i,Δ

_i with i=1,2;

α

₃,Δ

₃).

22. Device according to claim 21, wherein the second scaling means have been arranged for scaling by applying the second scaling factor as being a function of the reciprocal value of the second power related parameter raised to a first adjustment parameter (α

;

α

_i with i=1,2;

α

₃), the second power related parameter being increased with a value corresponding to a second adjustment parameter (Δ

;

Δ

_i with i=1,2;

Δ

₃).

23. Device according to claim 21 or 22, wherein the first scaling means include a scaling unit (42) for scaling the output signal by applying the first scaling factor, the first scaling factor (S(Y+Δ

);

S(Y+Δ

_i), with i=1,2) being a function of the first power related parameter increased by a value corresponding to a third adjustment parameter (Δ

;

Δ

_i, with i=1,2).

24. Device according to any of the claims 21,-,23, wherein the second scaling means have been included in the pre-processing means for scaling the output and reference signals (Y_S(t), X_S(t)) as scaled in the first scaling step, by applying the second scaling factor.

25. Device according to any of the claims 21,-,23, wherein the signal combining means include:

differentiating means (15) for determining from the representation signals a differential signal (D),

modelling means (16) for processing the differential signal and generating the quality signal, and

the second scaling means for scaling one of two signals by applying the second scaling factor, the two signals being the differential signal (D) as determined by the differentiating means (15) and the quality signal (Q) as generated by modelling means (16).

26. Device according to any of the claims 21,-,25, wherein the second scaling means include at least one scaling unit (43, 44;

51;

52) coupled to the first scaling means (42) for receiving the first scaling factor and for applying the second scaling factor as derived from the first scaling factor.

27. Device according to claim 25, wherein the second scaling means include a scaling unit (61;

62) for scaling said one of two signals by applying the second scaling factor, the second power related parameter of the second scaling factor (V<sup>α

3</sup>(Y+Δ

₃,t);

V<sup>α

3</sup>(Y+Δ

₃)) including an instantaneous value of the power of the output signal increased by an adjustment value corresponding to the second adjustment parameter (Δ

₃).

28. Device according to claim 27, wherein the second scaling means have been combined with third scaling means, which include at least one scaling unit (51;

52) coupled to the first scaling means (42) for receiving the first scaling factor and for scaling said one of two signals (D;

Q) by applying a third scaling factor (S<sup>α

i</sup>(Y+Δ

_i), with i=1,2), in combination with the second scaling factor, the third scaling factor being derived from the first scaling factor (S(Y+Δ

_i), with i=1,2).

29. Device according to any of the claims 21,-,28, wherein the first power related parameter of the first scaling factor includes an average power of the output signal.

30. Device according to any of the claims 21,-,29, wherein the first power related parameter includes a total time duration during which the power of the output signal is above or equal to a threshold value.